Deborah Haynes, foreign affairs editor

Spare a thought for the crew of a Royal Navy warship braving the threat of an Iranian attack to keep UK-flagged ships moving in the Gulf.

HMS Montrose, a Type 23 frigate, has been transiting back and forth through the Strait of Hormuz since Wednesday accompanying nervous groups of tankers.

France, Denmark and Italy have made positive noises about supporting this kind of mission and the United States is trying to build an international maritime protection coalition.

But only Britain is actually delivering the guard service despite a widely acknowledged and frankly inexcusable - Prime Minister Boris Johnson please take note - shortage of warships, ammunition, spare parts and sailors.

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Rear Admiral Alex Burton, a former Royal Navy officer, used Twitter to show his respect.

"If you think it's the #hottestdayoftheyear here then think of the outstanding HMS Montrose, at heightened alert state (sailors wearing LOTS of thick clothing) in temperatures of over 40 degrees, successfully delivering unwaveringly for Great Britain," he wrote on Friday.

Image:Iranian forces seized the Stena Impero tanker as it travelled through the Strait of Hormuz

The Royal Navy was tasked with providing what is effectively an escort service to British-flagged ships in the Gulf after Iranian forces seized the Stena Impero tanker as it passed through Omani waters on 19 July.

HMS Montrose was nearby but not close enough to come to the vessel's aid before it was forced to divert into Iranian waters and was boarded.

A recording was released of radio interactions between an officer from the British frigate, an Iranian official from one of the Iranian craft that accosted the tanker and the ship's master.

The British voice could be heard telling his Iranian counterpart: "You must not impair, impede, obstruct or hamper the passage of the MV Stena Impero... Please confirm that you are not intending to violate international law by unlawfully attempting to board."

The Iranian naval officer told the stricken tanker: "You obey, you will be safe. If you obey you will be safe. Alter your course to 360 degrees immediately, over."

Iran threatened to target British-flagged ships after Royal Marines helped to seize an Iranian super tanker off the coast of Gibraltar earlier this month.

Britain has accused the Grace 1 of transporting oil to Syria in breach of European Union sanctions. It is still being held.

Tehran called the seizure an act of piracy. Iranian forces have already nabbed one British-flagged tanker in return but what if they try to take another?

The Department for Transport has advised all British-flagged vessels to give them "sufficient notice" of their plans to move through the Strait of Hormuz. This is to enable the Royal Navy to ensure they can be accompanied - either individually or in groups.

It means a British warship should be present to deter another attack.

But it also increases the chances of an armed confrontation between Tehran and London if Iran's Islamic Revolutionary Guard Corps decides to take the Royal Navy on regardless.

A lone warship may appear to be a vulnerable target - it is - but the frigate is seemingly well armed and capable of defending itself and the vessels it is protecting.

Though it is not known what rules of engagement the vessel is operating under.

The US military, which has a significant deployment of warships and aircraft in the Gulf, is already supporting HMS Montrose with information gleaned from surveillance planes.

Perhaps it would also respond with force in an emergency but that is not clear.

What is really needed is for other nations with an interest in securing the Strait of Hormuz to stop prevaricating and start implementing plans to share the risk and the responsibility of protecting this waterway.Deborah Haynes

Any move by British or American forces to open fire on an Iranian target would be a significant escalation even if they are acting in self-defence.

What is known is that a second major British warship is finally due to arrive in the Gulf in the next day or so to allow HMS Montrose time for maintenance and a crew change.

HMS Duncan, a Type 45 destroyer, is bigger and better armed than the frigate it is replacing, increasing the deterrent effect.

But what is really needed is for all other nations with an interest in securing the Strait of Hormuz to stop prevaricating and start implementing plans to share the risk and the responsibility of protecting this waterway.

British-flagged vessels are particularly vulnerable, which is why Britain has been forced to act first.

But limpet mine attacks over the past three months - blamed by the United States on Iran, though Tehran denies involvement - have struck Norwegian, Saudi, Emirati and Japanese-flagged ships.

Image:European navies are reluctant to support US calls for a naval coalition in the Gulf

European navies are reluctant to support US calls for a naval coalition in the Gulf - dubbed Operation Sentinel - because the two sides' policies differ on Iran after President Donald Trump pulled Washington out of the Iran nuclear deal that Europe still supports.

Jeremy Hunt, in one of his final acts as foreign secretary, proposed the creation of a European-led maritime protection force in the region, keeping US support at arms-length.

But almost a week on from the announcement there is no sign of such an entity, with experts saying the United States is the only power capable of heading a coalition.

Either way, the time to act is now, unless Iran can show it is no longer a threat to international shipping by releasing the Stena Impero.

Sky Views is a series of comment pieces by Sky News editors and correspondents, published every morning.